Bats flit in and out of their invisibility cloaks in the evening glow reflected on the pond. And sometimes, in the skidding sunbeams of the morning, I may catch the iridescence of a kingfisher feeding on water beetles. This pond has become another stepping stone for wilderness. Local native flora and fauna has found its way in and flourished, increasing local biodiversity.
And of course there is the swimming. Our children are learning to swim in a healthy environment free from the unpleasant effects of disinfectants found in most pools. I imagine, one day we will look back and wonder how we ever thought it was reasonable to let our children swim in anything other than natural water. But there is a different way. And knowing what I know now, I could do it for considerably less. Organic pools work with nature to provide clean healthy water for swimming. Plants and animals in the pond condition the water without the use of chlorine or other disinfectants.
Instead, the water holds a vibrant and diverse ecosystem, teeming with micro-organisms that constantly filter and devour any human pathogen that has the misfortune to plop in. The key to promoting a diverse eco-system is to prevent one species from dominating the pond. In a poorly created pond the usual dominating big baddy is blanket-weed.
Blanket-weed Cladophora superphylum is the most common filamentous alga forming dense swathes over ponds in bright warm weather where phosphate and nitrate levels are high. The key to control the growth of algae is to restrict the nutrients entering the pool. If the nutrient level is low enough, plants successfully compete with algae. As the plants grow they accumulate the nutrients in their structure and further deprive the algae from flourishing.
As well as plants there are other vital allies — the myriad of micro-organisms that make up the zooplankton living in every cubic millimetre of pond water. Foremost amongst the zooplankton are daphnia.
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These tiny crustaceans are essential to promoting clear water by filtering out, and consuming, suspended particles of algae. We need to look after them. Algae will never disappear completely, after all they are wild plants and part of the healthy eco-system, but in a properly functioning pool most of the algae will be confined to the margins or hardly visible at all.
In the Organic Pool, the area is divided into two sections, the swimming zone and the regeneration zone. The regeneration zone contains the plants so is also referred to as the planted zone. The pool has the deep swimming zone in the middle surrounded by the planted zone. The planted zone should represent at least half of the total area of the pool, and it is here that most of the water conditioning occurs. The water is circulated throughout the whole pool. If a pool is large enough, with enough deep areas, then it can rely upon natural convection currents and surface wind movement to maintain the water circulation.
If the pool is smaller, or the regeneration zone proportion of the whole is reduced below half, then technical equipment can provide the circulation and filtration. Conventional chorine pools can expect a build-up of chemical residues, so the pool needs to be drained out and the water changed from time to time. This equates to a huge saving in precious water resources.
Because tap water contains chemicals that interfere with how a natural pond works, it is better to fill your pool with rainwater. All the rainwater that falls on our house is collected and pumped to the pool. Even better, it is quite simple to construct devices to divert the first flush of roof water away, reducing the amount of detritus making its way into the pool. It may still take many weeks or months to fill the pool, but if you are making the pool yourself, you will find that it fills up as you are working on the project. The laboratory water tests for my organic pool showed, not only was it perfectly safe for swimming, it was good enough to drink.
It comfortably exceeded drinking water standards in all parameters tested. He also runs courses for anyone interested in building their own Organic Pool. To talk pond stuff and drink loads of tea, log on to organicpools. Share Farmers are 7 times more likely to die from cardiovascular disease than other occupations. The beauty of the ponds is a big part of why visitors return the Vineyard year after year.
Many people cherish the ponds, although their economic value is hard to quantify. But housing booms and land-use changes over the decades have altered their composition, threatening to undo a delicate balance between people and the environment. The problem, at least, is clear: Too much nitrogen from septic systems creates an overload of nutrients entering the ponds. The resulting algae blooms consume oxygen and prevent sunlight from reaching aquatic plants at the bottom. When the plants die, so do the shellfish and other organisms that depend on them for food and habitat.
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On the Vineyard, declining shellfish yields at least since the s, and an array of reports and warnings from the scientific community seem to have reached enough ears for Island towns and organizations to finally be taking major steps to protect the ponds. But the future is far from certain.
Around 20, years ago, the Wisconsinan glacier, which had advanced from the north, began to melt, creating valleys with rivers flowing to the south. Dips in the road between Chilmark and Edgartown still indicate where those rivers once flowed. As the glacier continued to melt, the sea level rose, creating barrier beaches that impounded the meltwater.
The ice sheet moved slowly, in a series of small advances and retreats, scouring out pockets in the earth that later filled in with meltwater.
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That process formed the north shore ponds, which are geologically and ecologically distinct from their south shore neighbors. A unique balance of natural and manmade conditions affect each pond. As a result of more permeable soil along the south shore, the Great Ponds receive more groundwater. That, and the fact that they are closed to the ocean for much of the year, makes them more susceptible to nitrogen from septic tanks.
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On the north shore, where there is more clay, the ponds receive a greater proportion of their nutrients from runoff. But in both cases, the primary threat is nitrogen. And more development around Oak Bluffs and Vineyard Haven harbors over the years means more nitrogen around those ponds. European settlers began breaching the ponds in the s to create habitat for fish and shellfish. Today managed by town shellfish departments, the breachings still continue throughout the year, flushing out silt and pollutants and allowing the mixing of saltwater and freshwater.
During a typical breach in Tisbury Great Pond, about million gallons of water rush into the ocean each day. Eventually there is a free exchange of seawater and freshwater. After a few weeks, the cut usually closes as sand carried east by the ocean currents rebuilds the barrier beach. Most of the north shore ponds have been permanently opened to support fisheries.
Kennedy believed the periodic breaches were at least partly why the ponds here are in such better shape than those on the Cape. He added that most of the Great Ponds are healthier than those on the north shore. Island ponds are in relatively good condition, Mr. But some paint a more troubling picture. Fifty years ago, shellfish harvests on the Vineyard, as well as on the Cape and Long Island, were perhaps twice what they are today, said shellfish group director Rick Karney.
Lagoon Pond is widely considered the most problematic, he said, due to its poor circulation and denser development. Like other north shore ponds, it is permanently opened, but the opening is relatively small. At the other end of the spectrum, Cape Pogue on Chappaquiddick has almost no development, but excellent circulation.
It is often hailed as having the best water quality and shellfish harvests on the Island. Kennedy said, noting the effects of nitrogen on dissolved oxygen and sunlight. Paid for by towns and the state, the reports provide exhaustive analyses of each pond, and a recommended daily limit for nitrogen. Eelgrass supports a variety of pond organisms, including scallops, which attach to the stalks as juveniles. It also aids in sedimentation and can act as a buffer for waves.
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Eelgrass and clear water go hand in hand. Most ponds here still have some eelgrass, Mr. Vineyard ponds are experiencing a range of impairment, from moderate to severe, according to the MEP. As might be expected, eelgrass is more abundant in the northern and eastern ponds, which are more open, and less abundant to the south and west. In some cases, the solutions are relatively straightforward.
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In Oak Bluffs, the installation of two eight-foot culverts in Farm Pond, a smaller estuary to the east of the Lagoon, is expected to improve flushing and achieve the MEP nitrogen threshold. But for the Lagoon, with poor circulation and denser development, sewering may be unavoidable. The MEP recommends a nitrogen limit of. Town officials in Tisbury and Oak Bluffs believe that will require decades of work and millions of dollars to achieve. Howes said that all of the data has been collected for Menemsha Pond and several ponds in Edgartown, including Cape Pogue.
He hoped to complete the report for Menemsha Pond this summer. While those numbers do not reflect the full range of benefits the ponds offer, shellfish revenue may be the most concrete measure of their value. Conversely, he said, declining water quality would almost certainly lower property values. Conservation efforts have greatly limited new development in the Great Ponds area, Mr.